The disclosed system relates to electrical devices and more particularly to the protection of electrical devices.
Vehicles, such as cars, trucks, recreational vehicles, motorcycles, truck tractors, motor homes, three-wheeled vehicles, snowmobiles, motorboats, aircraft and others each include electrical devices. Typically, these electrical devices are powered by an on-board battery. Batteries in general store energy in chemical form that is released upon demand as electricity. The electrical power is used by the vehicle's ignition system for cranking the engine and may power lights and other accessories. Further, should an alternator belt fail, the battery might also need to power the vehicle's entire electrical system for a short period of time. Automobile batteries are typically twelve volt direct current batteries and supply power over a fairly wide range.
Automobile batteries are often rated in terms of cold cranking amps, which is the ability of the battery to supply an amount of current for 30 seconds at zero degrees Fahrenheit without dropping below a specified cutoff voltage (this is manufacturer specific and can range from 7.2 volts to 10.5 volts). Cold cranking amps for car batteries can range from about 500 amps to about 1,500 amps. Further, smaller batteries for motorcycles, mopeds and other small vehicles can provide amperages as low as twenty-five amps.
As more and more complicated electrical systems are placed into automobiles, the need to protect those devices within those systems as well as to protect the automobile battery will increase. There is also significant work being done to develop a 42 volt automobile generator that would drive a 36 volt battery for higher voltage loads. As voltages of batteries increase, the potential damage also increases. It is therefore desirable to provide a device that protects a vehicle's electrical system when a short circuit or overcurrent condition occurs.
Another problem associated with vehicle batteries, such as automobile batteries, is load dump. The main battery line in an automobile is the source of a number of potentially harmful transients, including load dump. One form of load dump occurs when the connection from the generator or alternator to the battery is broken. The generator in that time continues to provide power and because the battery is not connected to the generator, the power runs into the voltage regulator causing a voltage rise. The mechanical generator typically needs several hundred milliseconds to bring the overvoltage situation under control, but during that time it is possible for the voltage to rise as high as 200 volts. Another form of load dump occurs when a battery cable is suddenly disconnected from the battery. Such a situation can cause overstresses of electronic parts connected to the battery due to the inertial energy within the vehicle's electrical system. A need therefore exists to protect vehicle devices connected to the battery from the dangers due to overvoltage caused by load dump.
Also, as automobiles add electronics to historically mechanical devices, the potential danger upon an accident or other type of catastrophic vehicle event, such as a fire, increases. It is desirable to discontinue power to many electrical components upon such an event. For example, many automobile fuel systems are now controlled electronically. It is desirable to discontinue power to the fuel system upon an accident or catastrophic event to stop the flow of fuel and to minimize injury and damage. Further, an accident can often cause a wire's conductor to be exposed, wherein the exposed wire can then contact the vehicles chassis and cause a short. The short in turn heats and melts the electrical insulation, potentially causing a fire. A need therefore exists for a device that discontinues power to certain electrical vehicle components. On the other hand, it is desirable to maintain power to other components and functions of the vehicle upon an accident or catastrophic event, such as the automobile's flashing lights, door locks, cellular telephone, etc. Accordingly, the device should accommodate that need as well.